© Galloway Astronomy Centre 2016
All images are copyright – M Alexander unless otherwise stated
Tel: 01988 500594
Improving Your “Cheapy” Telescope
Low cost telescopes of say £50 to £120 don’t tend to be very
good quality. These are the type you can buy in department
stores, some camera shops, ebay and even supermarkets.
If you have one of these there are a few things you can do
straight away to improve it.
All the parts as indicated in Image #1 that make up a telescope
are important not just the tube you look through.
A brief extra note - in the Image #1 you
will see a ring with a hole in it at the
front of the telescope. If after you
remove the front cover you still see this
on yours stick your finger in the hole and
hook out the rest of the cover. It should
pull away easily. The front of your
reflector should look like image #2. The
whole of the cover should be removed
every time you use the telescope. (I only
mention this as I see it all the time)
Cheap telescopes often have Altitude -
Azimuth mounts (AZ mount) which can be a
bit flimsy and wobbly. See Image #1. These
points will improve an equatorial mount (the
type with a counter weight) too.
The wobble is mostly due to the tripod legs
not being held rigidly. Avoid extending the
tripod legs too high as this makes the wobble
worst. The thin metal leg braces and
accessories tray which should help stabilise
the mount often have little effect. Also avoid
using the telescope on a hard surface like
concrete, on grass push the spikes on the end
of the legs into the ground.
Try each of the following one at a time as just
one might be enough:
- Replace the tray with a larger triangular piece of 2 mm thick
plywood (shaped as in Image #3) this will hold the
legs rigid. The flat corners need to be the width of each tripod
- Tighten all wingnuts and screws on the tripod firmly without
over tightening to minimize flex in the whole structure.
- To minimize vibrations hang a large plastic container with a
handle like the ones for milk or fabric conditioner and half fill it
with sand. Now hang it from the centre of the mount.
By the way, you should not really use the tray to hold your
eyepieces - it allows them to get cold and damp.
Better to keep them in your pocket with the covers on
Your telescope is almost certainly has a tiny finderscope. As you
can see from the picture (image #4) it looks like a mini telescope
mounted on top of the telescope itself. There is are hidden
problems with this type of finderscope.
1) The small lens visible at the front of the
finderscope does not let in very much of the
light you need to be able to locate the objects
you want to see.
2) Worst still if you look closely just behind
the lens is a disc with a small hole in the
centre. This further restricting light entering
your eye. It is there to stop bright objects like
the Moon and planets from having a rainbow of
colours around them as the lens is of poor quality. However, the
colours are not really much of a problem, better to take it our and
let in more light.
Removing the baffle is very easy to do following these steps:
- First unscrew the end you view through from
- Looking inside the now open end of the tube
you will either see a small black disc close to
the lens or a short black tube (see image #5)
- Now unscrew the front fitting that hold the
lens in place. Do this with the tube vertical
and the lens end at the bottom. This is so the
lens does not fall out. Don’t worry if it does,
looking at it you will see the lens is flat on one
side and curved on the other. Drop the lens
back in with the curved side down.
- Now using a pencil or metal rod that is long enough you can
knock out the disc (or tube) baffle.
- Reattach the front lens end then the viewing
- Looking through the finderscope it should be
noticeable how much bright is the view.
You may not be aware that the finderscope
can be focused. From Image #6 you will see
that the end you look through rotates in both
directions separately to the part that you
detached to get inside to find the baffle. To
focus the finderscope point it toward a distant object and rotate
the lens end until the image is sharp.
There is another option - replace the
finderscope with a red dot finder with a 2 hole
base (Image #7).
The same type of finderscope is fitted to many
Skywatcher telescopes. It works by putting a
red dot onto a clear screen which you look
through, you put the dot on the object you
want to observe. As with the finderscope it
needs to be aligned with the telescope.
The focuser is the part into which you put the
eyepieces to view through the telescope (see
Image #8). There is a small knob on either side
which rotates to move the eyepiece in and out.
This can feel stiff which will cause you to shake
the telescope making accurate focusing difficult.
Between the two knob on the underside will be
two (or four) cross headed screws. Unscrew all
the screws by about a half turn, that should give
a smoother feel to the focus. If you unscrew
them too far you will see the focuser knobs are
able to wobble up and down. Just tighten the
screws a little until the wobble stops.
Eyepieces (please don’t call them lenses) are
extremely important as they provide the
magnification you need to view the object.
There are several common problems with the
eyepieces supplied with cheap telescopes:
1) Some eyepieces are non standard 0.965”
diameter. They should be 1.25” diameter. See
2) they have often tiny lenses so you have to
get your eye very close to the lens look
through it. This is a particular problem if you
3) the magnifications they achieve do not
always give the best views.
If the instruction sheet does not tell you the
diameter of the eyepieces you can easily check by
holding a ruler across the chrome tube of the
eyepiece. If it is less than 1.25” then you have
0.965” eyepieces. These need to be replaced as
soon as you can.
Obviously a 1.25” eyepiece will not fit straight into a
0.965” focuser - an adapter (see image #10) is
required allowing the telescope to take the larger
See the bottom of this page for alternative eyepieces.
Magnification (M) can be calculated by
M= focal length of the telescope
focal length of the eyepiece
For example a telescope of 700mm focal length (FL) and an
eyepiece of 4mm gives you an M = 175 (ie 700/4). This is
written as 175x - meaning 175 times magnification
For a telescope of 70 or 76mm diameter this is much too high.
The image will be faint and probably will not focus sharply.
The good guide to the maximum magnification of any telescope
can be found by dividing the aperture (telescope front lens or
mirror diameter) by 25 then multiply by 30
eg 76mm reflector telescope
76/25 = 3
3 x 30 = 90
If your maximum magnification does not exceed 90 your
telescope will give you enjoyable bright, sharp views.
Use the first calculation to see what magnification each of your
eyepieces will give. Your kit may also include a 2x (or 3x) Barlow
lens. This is a special lens which when used with an eyepiece
doubles (2x) or triples (3x) the normal magnification of that
Here is an example of the above:
You have a 76/700 reflecting telescope - this means the mirror is
76mm in diameter with a focal length of 700mm
There are 3 eyepieces with labels reading 20mm, 12.5mm & 4mm
- this means focal lengths of these eyepieces are 20mm 12.5mm
There is also a 2 x Barlow - this will triple the magnification of
any of the eyepieces
20mm + 2x Barlow
12.5mm + 2x Barlow
4mm + 2x Barlow
You may think a magnification of 35x will not show you much, but
it depends on the size of the object. The Moon will show a lot of
detail and allow you to decide where you what to look more
closely. If you have not too much light pollution large star
clusters will fill the view.
As you will see the 4mm eyepiece on its own far exceeds the 90x
maximum for this size of telescope. Although the use of the
Barlow lens with the 12.5mm eyepiece exceeds this, on bright
objects like the Moon you may find the view is OK.
A quick calculation will show that a 20mm eyepiece with a 3x
Barlow lens gives 105x magnification, which means you could not
use it with any of the other eyepieces.
A quick search of the internet for Eyepieces will soon show you a
confusing number of types and focal lengths, so which one is best
for you? First off don’t spend a huge amount on an eyepiece. An
eyepiece costing as much as your telescope will not improve the
view as much as you might hope. It is more sensible to save that
money for a better telescope in the future. Nor do you need a box
full of eyepieces - two or at most three covering low, medium and
high magnification is all you need. If you are happy with the
20mm eyepiece that came with the telescope why replace it? It is
the mid and high magnification eyepieces and probably the
Barlow lens too that usually need replacing.
So what other sizes do you need? You can work it out by
reversing the magnification equation.
Eyepiece FL = Focal length of the telescope
Eg You want 90x magnification
700/90 = 7.7mm
Eyepieces FL are usually whole numbers so you cannot buy a 7.7
mm eyepiece only a 7mm or 8mm. Rather than buy one that size
you can achieve the same magnification using the Barlow lens
and you get the advantage of the lower magnification using it on
its own too. Therefore, I would suggest a 15mm eyepiece. This
gives 47x on its own and 94x with the Barlow lens.
If the 20mm eyepiece is just adequate, but you would like to
change it then buy a 25mm eyepiece as it will give you lower
magnification and a larger field of view to locate an object. A
25mm eyepiece gives 28x on its own and 56x with the Barlow
lens. This later is the same as the 12.5mm eyepiece that came
with the telescope so you have effectively replaced that too.
So with just two new eyepieces and possibly a new Barlow lens
you have a wide range of magnification from low to the maximum
the telescope can easily handle.
The industry standard for eyepieces is a barrel diameter of 1.25”
so they can be used in any telescope you buy in the future.
How much do eyepieces cost?
We have a special offer for you:
Basic 2x Barlow Lens
Higher Quality 2x Barlow Lens
Red Dot Finder (2 hole type)
0.965” to 1.25” Eyepiece Adaptor £12
Delivery charges apply
If you need any help or advice on modifications, eyepieces
or buying a new telescope please contact me.